You're using logic to say why that shouldn't be the case. There is no logic to presidential pardons, it's an aberration, an arbitrary judicial power given to an executive.
Quite frankly, if the constitution doesn't explicitly deny it, I don't see why a self pardon shouldn't be possible.
Ivanka could do that you just described and there would be no argument about the legality of the pardon.
If he indeed pardoned himself, it will boil down to wherever the wind is blowing in the supreme court when they adress the case.